The present invention relates to improved threaded spacers for use in joining adjacent sections of drill pipe in a drill string for recovering oil or gas from a subterranean formation, as well as an improved method for making such threaded spacers.
In order to prevent thread galling and to provide joint security in connection with the joining and use of drill pipe used in oil and gas recovery, the threads of the pipe are typically coated with a suitable thread compound. These compounds usually contain finely divided metal powder such as zinc or lead and sometimes other ingredients such as active sulfur. Experience has shown that these compounds may degrade over time, or under the influence of the extreme conditions encountered in use, leading to loss of their anti-galling properties. Furthermore, many of these compounds are now classified as hazardous substances because of their high metal particle content.
In order to eliminate these problems, Italian Patent 980421 to Baryshnikov et al. describes a threaded spacer which is intended to replace conventional thread compounds. The particular threaded spacer disclosed is composed of a conical section having a flange at its open, larger end. Cooperating helical grooves are formed in the inside and outside surfaces of the conical section wall such that the conical wall, as a whole, is undulating in cross section. The flange, which is arranged perpendicular to the axis of the conical section, is made about 8 to 16 times as thick as the conical section wall. With this structure, the conical section of the spacer can be received between mating grooves of adjacent drill pipe sections, while the flange will fill the annular space defined between the shoulders of adjacent pipe sections.
The threaded spacer of Italian Patent 980421 is described as being made from copper/beryllium alloy. This alloy has a unique combination of properties, including wear and galling resistance, when mated with steel and other metals. It is therefore claimed that this device can totally replace conventional thread compounds, thereby eliminating the environmental and performance problems associated with these compounds.
Unfortunately, Italian patent 980421 appears to be a conceptual disclosure only. No method of manufacture is disclosed. Nor is the description of wall thicknesses clear.
Other devices for use in drill strings, such as drill collars, drill bit bushings, centralizers, shock collars, directional tools, and xe2x80x9csubsxe2x80x9d (couplers for attaching drill bits to drill strings), are currently made from copper/beryllium alloy. These devices are typically made by machining, i.e. operations in which a portion of the work piece is removed by cutting, drilling or like operation. Accordingly, it appears possible that the threaded spacers of Italian Patent 980421 can be made by machining as well. However, machining is inherently expensive, especially when a complex part is made from an expensive material such as copper/beryllium alloy. Furthermore, it is difficult to make parts having extremely thin wall sections by machining operations.
Accordingly, there is a need for a new method of making threaded spacers of the type shown in Italian Patent 980421, which avoids or at least minimizes machining steps in forming the basic part structure. In addition, there is also a need to develop threaded spacers having thinner wall sections and thicker wall sections than contemplated in that patent.
In accordance with the present invention, a new process is provided for making threaded spacers of the type shown in Italian Patent 980421. In this process, a strip or sheet of metal is mechanically deformed in a first forming step to produce a preform having the gross shape of the desired threaded spaced product including a thin-walled conical section and an integral flange. Then, in a second forming step, the preform is mechanically deformed again to impart helical grooves and an undulating cross-section shape to the thin walled conical section of the preform, thereby producing the desired threaded spacer product.
In both forming steps, forming is accomplished by mechanical deformation without machining. Therefore, the desired threaded spacer product can be formed easily and inexpensively and hence at a cost which makes its use economically feasible. Furthermore, threaded spacer products having much smaller wall thicknesses than possible in the past can be made using this approach. This further contributes to a reduction in manufacturing cost, because the amount of expensive beryllium/copper alloy used is greatly reduced.
Thus, the present invention in one embodiment provides a novel process for making a thin walled threaded spacer for use in joining adjacent sections of drill pipe, the spacer having a hollow conical section and an integral spacer flange, the wall thickness of the hollow conical section being about 0.5 mm or less with the spacer flange being about 5 to 40 times as thick as the conical section wall thickness, the spacer conical section defining cooperating helical threads for mating with the threads of adjacent sections of drill pipe, wherein the process comprises mechanically deforming a strip of metal to form a preform defining a preform conical section and an integral preform flange in a first process step and then further mechanically deforming the spacer conical section to impart helical threads on its inside and outside faces, thereby forming the desired threaded spacer product.
In another embodiment, the present invention also provides an improved thin walled threaded spacer for use in joining adjacent sections of drill pipe having helically-threaded male ends and helically-threaded female ends, the inventive spacer being formed from a copper/beryllium alloy and having a hollow conical section defined by a conical wall having an inside face and an outside face, the thickness of the conical wall being between about 0.5 mm or less, the hollow conical section defining a smaller open end and a larger open end opposite the smaller open end, the spacer also defining a flange integral with the spacer conical wall at its larger end, the thickness of the flange being about 5 to 40 times the thickness of the conical wall, the inside face and the outside face of the spacer conical section each defining cooperating helical grooves such that the spacer conical wall is undulating in cross-section whereby the spacer conical wall can be received by mating helical threads of adjacent sections of drill pipe.